The prevalence of familial forms of transmissible spongiform encephalopathies (TSEs) particularly of the Creutzfeldt-Jakob disease type is unknown. Molecular genetic studies of patients and their families is of interest in order to (1) determine the distribution and types of point mutations in the PRNP gene worldwide; (2) to discover new mutations associated with these diseases; and, (3) to determine the association of the various types of mutations with disease phenotypes and clinical expression. During the period covered by this report we conducted collaborative studies on a worldwide basis and received more than 500 blood specimens for analysis from patients carrying a presumptive diagnosis of CJD, GSS, and/or FFI. In conducting these studies we broadened our procedures to search for other as yet unidentified mutations in addition to those most frequently detected at codons 178, 200, and 210. This expanded approach has resulted in the recognition of three new mutations, one at codon 150, one at codon 180 and one at codon 187. The codon 150 mutation had previously been reported in only two Japanese families and this is the first report of its occurrence in the United States in a non-Asian family in which there was no known family histoy prior to our findings. We have identified a large American-Italian family with a mutation at codon 102 in which there have been eight cases of GSS. One living family member carrying the codon 102 mutation (Proline<Leucine) was diagnosed clinically at age 27 as early onset Alzheimer's disease. The patient is currently 37 years of age, is fully demented, is in a nursing home and is the mother of three children. The geneology of this family shows that the diease is 100% penetrable. Western imunoblotting of extracted PrPres revealed a unique banding profile that may serve as a molecular marker for GSS. The banding pattern showed distinct unglycosylated fragments of PrP at 8 and 14 kDa. Densitometric analysis revealed that the relative proportions of the three major glycoforms were significantly different than those of sporadic or iatrogenic forms of CJD.